Instrumentation Study on Solar Energy Conversion system into Hydrogen Using Low Temperature Reactive Ceramics

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Converting solar thermal energy to hydrogen energy is expected to be an innovative method for solar energy utilization in the next century because theoretical conversion efficiency of concentrated solar thermal/chemical energy is up to 70%.Concentrated solar energy/hydrogen energy converter of the low-temperature operation type was constructed in order to utilize heat/chemical energy conversion system using the low temperature reactivity ceramics which has been established until now, and the conversion efficiency of solar energy to hydrogen energy in Japan (Tokyo) was measured by using this equipment.When the Boudouard reaction was performed using the beam down concentrator with an elliptical mirror, the temperature of about 1000℃ was stably obtained, and ca. 50% of COィイD22ィエD2 was reacted to generate CO. As the results of the CO generation rate, it is demonstrated that solar energy of 7 W (max : 10 W, conversion efficiency : 30%) is converted to chemical energy. Thus, this concentrator is suitable for the solar thermochemical process, and in addition, solar/chemical energy conversion efficiency can be obtained up to 50% (theoretical value : 80%) by improvement of the equipment.Water splitting reaction by FeィイD23ィエD2OィイD24ィエD2/NaィイD22ィエD2COィイD23ィエD2/HィイD22ィエD2O system was also carried out using the solar concentrator. In the XRD pattern of the reaction product, the peaks of NaFeOィイD22ィエD2 was observed, indicating that the reaction proceeded. The amount of generated hydrogen is almost correspondent to that of magnetite putting into the reactor, though a part of the stainless steel used as a reaction tube was also reacted to produce hydrogen.Development of cavity-type reactor to obtain high solar/chemical energy conversion efficiency is now in progress.